I would like to better understand the reasoning behind what the author says here:

A balanced 16-cavity mold costs 3-4x more than a single-cavity mold but only produces 16x the parts, which is why they only make economic sense above 500,000 units.

I guess if a single cavity mold costs $30,000 and a 16 cavity mold costs $110,000 you have an additional expense of ~$80,000, divided over half million parts is 16 cents. So lets say somewhere from 5-10cents per part to go 16x faster. My numbers might be off a bit but seems in the ballpark. I also don't know much a lego brick costs to make in terms of materials/opex.